Electrophoretic method of coating wire with graphite



NOV- 27, 1951 H. w. RlMBAcH ELECTROPHORETIC METHOD OF COATING WIRE WITH GRAPHITE Filed oct. a, 1947 INVENTOR ATTORNEY 5 M-Maz TEMPE/erakr f/v Patented Nov. 27, 1951 ELECTRPHORETIC METHOD F COATIKNG WIRE WITH GRAPHITE v Henry W. l

to Westinghouse Rimbach, Bloomeld, N. J., assignor Electric Corporation, East Pittsburgh, Pa., a. corporation of Pennsylvania Application October 8, 1947, Serial No. 778,703 1 Claim. (Cl. 21M-181) This invention relates to the lubricationjof wire, especially in connection with the drawing thereof, and more particularly to the coating of such wire with graphite.

The principal vobject of myinvention, generally considered, is -to coat wire, particularly such composed of molybdenum or tungsten, with a rmly adherent deposit of graphite by electrophoresis, whereby improved results are obtained and the necessity for a binder eliminated.

Another object of my invention is to improve and cheapen the process of lubricating wire, and particularly molybdenum and'tungsten wire during the operation of wire drawing, by applying a'coating of graphite thereto by electrophoresis, desirably from an aqueous suspension .containing a small proportion of a wetting or surface active agent, thegraphite being very finely divided.

A further object of my inventionis to produce a wire having a smooth dense graphite deposit adhering tightly thereto,. whereby it is adapted for being drawn through a plurality of dies without .intermediate lubrication.

- Other objects and advantages of the invention will become apparent as the description proceeds.

Referring to the drawings -Il Figure 1 is an elevational view, partly diagrammatic, of apparatus which may be used in practicing my invention. Y i

Figure 2 is an enlargedsectional viewvon the line II-II of Figure 1. Y

Figure 3 is an enlarged sectional view on the line III-III of Figure 1.

Figure 4 is a detailedA elevational view of a rewindingreel which may be used as an alternative to that illustrated in Figure 1.

Figure 5 is an enlarged sectional view on the line V-V of Figure 4, in the direction of the arrows. I

VFigure 6 is a graph illustrating the relationship between the duration of the operation and the amount of graphite deposited on the wire being treated. A-

Figure 7 is a graph illustrating the relationship between the proportion of the graphite in the suspension and the deposit obtained.

Figure 8 is a graph illustrating the relationship between the voltage drop between the wire being coated and the associated electrode and the deposit obtained.

Figure 9 is a graph illustrating the relationship between the temperature of the graphite suspension and the deposit of graphitebbtained.

In the drawing of wire, and particularly such made of tungsten or molybdenum, ithas Abeen the practice to apply a coating of graphite to the Y Wire before passing it through a die. vThe .graphite suspension used to coat such wire was of such composition and viscositythat 'a coating .Pf-#he lubricant. remaris there# Tha-@ating I is then dried, when binders in the suspension such as agar-agar and brown sugar served to hold the graphite on the wire. y

In accordance with my improved method, here disclosed and claimed, graphite is deposited on such Wire by electrophoresis, as bypassing the wire through a special graphite suspension lin a cell containing an electrode which is negative with respect to the wire. Pure graphite is thereby deposited on the wire which is then dried. The character of the deposit is such that it adheres tightly without the use of a binder.

Referring to the drawing in detail, like parts being designated by like reference characters, and rst considering the embodiment of my invention illustrated in Figures 1, 2 and 3, there is shown a spool or reel II from which wire I2 is drawn, it being assumed in the present -instance that the wire is tungsten or molybdenum, but other wire may be so treated as desired. The wire passes through an electrophoretic cell I3, through which a suspension lli of graphite is being continually circulated, under control of valve 2U, as by means of a pump I5 through pipe I6. Valves Il and I8 may serve to divide the output from said pump between that ilowing to the cell l2 and that passing back to the suspension supply in containing tank I9, for the purpose of agitating said suspension and preventingV the graphite from settling. Additional or alternative agitating means, such as a pipe from which air bubbles escape, or an impeller rotating in the suspension may be employed if desired.

During the passage of the wire through the cell I3, it is maintained at a potential positive with respect to an associated electrode ZI, as by means ofa source of direct current 22 connected through a controlling rheostat 23, ammeter 24, and contact brush 25, to the wire at its positive side. Its negative side is connected through the conductor 26 to hollow generally cylindrical cathode 2|. A voltmeter 2l may be used to indicate the applied voltage, the variation of which may serve to adjust the amount of deposit on the wire. Because of the fact that the temperature ofthe suspension increases during the coating operation, a cooling device, such as a coil 28 which is immersed in the suspension contained in tank I9 and through which cold water is circulated, may be employed to maintain the temperatureY as desired. The rate of circulation of the waterin the coil 28 may be controlled thermostatically.

The wire emerges from the cell I3 and passes on through .a heater 29, which may be in the form of a tube surrounded by a coil of wire heated to a controlled temperature from a source of potential 3I. After being dried, the wire passes over pulley 32 and is rewound on spool or reel 33, the speed of which i5 controlled by a variable speed drive, 34. When I first started with my experiments in 3 Y electrophorizing graphite to directly coat wire, I used 1% graphite in a mixture of four parts of water and one part of ethyl methyl ketone, to -1 which about 1% of diglycol stearate and 1% of ammonia had been added. I was able to successfully deposit graphite from such a suspension.

One disadvantage was that diglycolstearate was Y natos and vthe alkyl sulfonates, may be substituted. Because such graphite is when bought very finely divided, I find that no additional milling is needed. The maximum average particle size of thev graphitepreferred is 3 microns. Maximum ash vcontent is 1.0%. Other equivalent forms of graphite may be employed.

During the coating operation, the wire preferably leaves the spool H under xed tension. A source of direct current up to 150 volts should be available. The wire desirably passes along the axis of the coating cell and the desirably hollow cylindrical electrode 2| is preferably coaxial therewith and connected to the negative side of the source of power. The electrode 2| may be formed of molybdenum, about inch in diameter and 5 inches long. The tube furnace 29 heats to machine can also be used to vary the weight of coating. However, the wire, as lubricated in accordance with my invention, may be passed directly to a multiple-die machine, as in connection 4with the colddrawing of such wire through a plurality of dies without intermediate lubrication,

a relatively low temperature, merely suicient for deposit in accordance with the accompanying .l

graphs will be obtained.

The chief variables recognizable in the application of the graphite coating are duration of Y treatment, the effect of which is illustrated in Figure 6; percentage of graphite in suspension, ,A

the effect of which is illustrated in Figure 7; applied voltage the effect ofl which is illustrated inFigure 8; and temperature of the suspension in the cell, the effect of which is illustrated in Figure 9. It will be noted that the weight ofthe deposit is almost a straight-line function of the coating time and percentage of graphite in suspension. The ratio of weight of therdeposit in mgms. to voltage, increased from .05 at volts to .3 at 150 volts. Under the conditions of this test serious gassing was encountered at voltages much in excess of 150.

Temperature variation has little effect on the weight of deposit, but coatings become denser and more coherent as the temperature is increased. The adherence is also improved by the oxide layer formed on the wirev during the coating, because of said wire being maintained positive with the consequent liberation of oxygen by electrolysis. A preferred current drawn through the suspension is about 8 amperes per square inch of wire surface.

It will'be evident from the foregoing that my v as described in the Brush et al. application, SerialNo. 699,032, led September 24, 1946, and owned by the assignee of the present application.

The following is a typical comparison between the performance of Aquadag lubricated wire (see the Benbow Patent No. 1,168,050 as mentioning this lubricant) and wire coated with graphite by electrophoresis in accordance with my invention. The tests were run on a motordriven tensile strength machine. In both cases the wire was cold 40 mil molybdenum:

This shows thatr the application of graphite by electrophoresisv greatly decreases the friction of wire-drawing.

Instead of rewinding on a horizontal reel 33, as illustrated in Figure 1, the wire after coating may be wound on a vertical reel 33a as illustrated in Figures 4 and 5. That is, the-wire after passing from pulley 32, may bel connected to a slider 35 which moves upward freely in slot 36 in the peripheral portion of reel 3 3, turned counterclockwise as represented inv Figure 5` by any suitable mechanism.4 As the wirev is wound up, that is, from the position represented in full lines in Figure 4 to that represented in dotted lines in the, same figure, it passes to said reel at a definite elevation, the elevation of the, slider-connected portion'of said wire continually changing.

Although preferred embodiments of my invention have been disclosed, it will be understood that modifications may be made within the spirit and scope Of the appended claim.

I claim:

The method of coatingY wire comprising passing said wire through a bath consisting of about 1% of graphite suspended in a solution consisting of water and about .3% of wetting material of the group consisting of alkali metal salts of the alkyl aryl sulfonates and the alkyl sulfonates, and electrophoretically depositing graphite thereon with said wire connected as an anode.

HENRY W. RIMBAOH.

REFERENCES CITED UNITED STATES PATENTS Number Name Date 1,168,050 Benbow Jan. 11,1916 1,589,329 Sheppard et al. June. 15, 1926 1,702,927 Bezzenberger Feb. 19, 1929 1,724,134 Iredell Aug. 13, 1929 1,995,528 Williams Mar. 26,` 1935 2,089,883 Ellsworth Aug.. l0, 1937 2,111,575 Stack Mar. 22,1938 2,138,938 Plensler Dec. 6, 193,8 2,217,383 Robinson Oct. 8. 1940 2,236,861 Widell Apr. 1, 1941 

